Crystal violet and 2 nm gold nanoparticles were incorporated into medical grade silicone polymers by use of a novel two-step dipping strategy using water and water-acetone mixtures. Optical microscopic examination showed that the optimised polymer incorporated dye close to the polymer surface, with minimal dye encapsulation throughout the polymer bulk. The modified polymer was stable under aqueous conditions with negligible leaching of crystal violet from the polymer into surrounding aqueous solution at 37 uC. Exposure of the modified silicone to low power 635 nm laser light induced the lethal photosensitisation of both Staphylococcus epidermidis and Escherichia coli. Despite the laser used not matching the absorption maximum of the crystal violet-containing silicone samples, the lethal photosensitisation was the highest reported, in terms of bacterial kill per energy dose. Furthermore, surprisingly, some statistically significant dark kill was also noted.

Photosensitisation of polymers has important potential clinical applications such as the prevention of catheter-associated urinary tract infections (CAUTIs). Polymers incorporated with methylene blue (MB) and 2 nm gold nanoparticles (AuNPs) are effective in killing bacteria at the surface following low power visible illumination. Studies of medical-grade silicone polymer samples including segments from urinary catheters were carried out to investigate the generation of reactive oxygen species and the involvement of Type 1 and 2 mechanisms. Singlet oxygen was observed using direct phosphorescence detection and hydroxyl radical generation using electron paramagnetic resonance (EPR) spectroscopy; we conclude that both Type 1 and 2 mechanisms can operate with polymeric photosensitisation. Transmission electron microscopy (TEM) directly demonstrated the incorporation of AuNPs at the surface of the silicone. Using silicone doped with MB AuNPs, a $3 log 10 reduction in the number of viable Staphylococcus epidermidis bacteria was achieved when exposed to low power laser light; prior sterilisation with ethylene oxide (EO) had no influence on efficacy.

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